Does petrol go stale?

[Golfer1]

Well I am now eight months down the line with my Excel Plug in Prius, I have done 5000 miles on one tank of petrol and I was wondering whether over this time span does petrol goes off and lose some of its qualities, on my second refill I have used Shell super unleaded thinking that this might help.

I have experienced exceptional fuel economy my last longish round  trip I did 280 miles and averaged 95.8 miles to the gallon. This was cruising between 40 to 65 mph when I could. Another small round trip of 70 miles, coming back, just on regenerative Battery alone, I achieved 96 mpg. Fantastic!

 

 

[TheProfessor]

When stored in a sealed container, petrol does not deteriorate.

 

However, when stored in something that's open to the air then it can. This is mostly caused by the ethanol, which is often added to petrol, releasing water as it comes in contact with the air. The water sinks to the bottom of your tank (as it's more dense than petrol) and then enters the engine where it can cause issues. Also, other additives, can also deteriorate or evaporate in contact with air, which reduces the quality of the petrol. It's these additives you're paying the extra premium for when you chose Shell (other than ethanol).

 

Now a car's fuel tank is reasonably, but not perfectly, sealed from the air. At the very least, it must take in air as the fuel is used.

 

So how long will it last in a car before going "bad" is anybody's guess, buy I would imagine a long time. Months to years.

 

 

 

 

[altocumulus]

I have had the same thought over the years, more so now I have a phv. I would hope Toyota factor such issues into their calculations! Mind I do add an additive to petrol I store for lawnmower and brushcutter...

[QuantumFireball]

In the manual for mine:

Quote

For plug-in hybrid vehicles, fuel may remain in the tank for a long time and undergo changes in quality depending on the how the vehicle is used. Refuel at least 20 L (5.3 gal., 4.4 Imp.gal.) of fuel every 6 months (refuel a total of at least 20 L [5.3 gal., 4.4 Imp.gal.] over a 6-month period), as this may affect components of the fuel system or the gasoline engine.

 

[altocumulus]

Chuckles - One day, perhaps, I'll have a closer read of the manual!

[Mick F]

People say that leaving petrol in a lawnmower or a chainsaw for months, it goes stale.

Not in my experience it doesn't.  Unleaded or 2Stroke, all works well after months sitting in the machines in the shed, and I have had many many over the years ........ and still have.

Mick.